Until today, active components to be used as an agricultural chemical having insecticidal, fungicidal or herbicidal activity have been formulated into a wettable powder, an emulsifiable concentrate, a suspension concentrate, dust, etc. and have been used in such a formulation form depending upon the physical and chemical property and the application purpose. However, among the formulation types described above, an emulsifiable concentrate has a problem of environmental pollution caused by organic solvents contained therein, and a suspension concentrate has a problem of easily causing separation of the components into phases during the preservation for a long time since the active ingredient(s) is dispersed in an aqueous solvent used for the formulation. Further, a wettable powder formulation and a powder formulation has a problem in safety for human bodies as they easily cause the dusting at the production process and at the places to practically use them. Due to such problems, several water dispersible granule formulations have been provided recently in order to settle such problems.
Normally, the water dispersible granule formulation is prepared according to so-called extrusion method, which is combining a solid active ingredient, a carrier comprising minerals in fine powder, surface active agents, etc., pulverizing the combined mixture by using a dry mill, then adding bound water to the mixture and kneading the mixture by using a kneader, and forcibly extruding the kneaded mixture to pass it through a multiporous plate containing a plurality of pores with the diameter of 0.5-2.0 mm.
However, if the active ingredient has a low melting point, or if the active ingredient has a peculiar property of being hardly pulverized into fine particles, dry milling method has not been applicable for such use.
In addition, in case of dry milling method, the particle size of the pulverized components in a formulation is normally in a range of from 5 to 20 μm, thus it is difficult to pulverize the components into a size ranging from 3 to 5 μm or less so that there is a problem that the dry milling method cannot be used for the production of the water dispersible granule, particularly when the active ingredient has a low melting point, or the active ingredient is required to be pulverized into fine particles ranging from 3 to 5 μm or less in order to enhance the biological activity.
Generally, contacting area of an active ingredient with a growing plant gets small when the particle size of the active ingredient is coarse, and the total amount of the active ingredient attached onto vegetable leaves is reduced. For example of an insecticide, the initial insecticidal activity, namely the activity just after the application of the insecticide, may be deteriorated because the penetrating amount of the active ingredient into leaves and the contact frequency between a pest insect and the active ingredient particles on leaves may be generally reduced.
As a formulation process for resolving the problems as described above, a process to formulate a water dispersible granule is known, where an active ingredient for an agricultural chemical is pulverized into fine particles under wet milling, kneading the ground active ingredient with a carrier consisting of minerals, and granulating the obtained mixture by extrusion. (See, for example, JP laid-open 3-146126 gazette).
However, when an active ingredient which may be easily decomposed owing to environmental conditions is used for production of a water dispersible granule by kneading the active ingredient with a carrier consisting of minerals following to the wet milling of the active ingredient and then granulating the kneaded product, the residual activity of the active ingredient tends to be remarkably deteriorated due to decomposing effect given by light, water and the like since the particle size of the pulverized active ingredient into fine particles is generally so small as much as 1-5 μm.
Furthermore, constraint of water supply at the wet milling is imposed due to the required amount of bound water at the kneading, thereby further constraining the amount of the active ingredient to be subjected to the wet milling, which has made hard to produce a water dispersible granule containing high content of the active ingredient.
Therefore, if the active ingredient is required to be pulverized into fine particles to enhance the biological activity and is the one that is easily decomposed owing to environmental conditions, it is difficult to obtain a water dispersible granule formulation provided with high initial and residual activities according to a conventional process for preparing water dispersible granule formulations.
Besides, in such cases that (1) a water dispersible granule contains different active ingredients and one of which cannot be pulverized into fine particles by dry milling method, and (2) a water dispersible granule contains different active ingredients, one of which is required to be pulverized into fine particles by wet milling in order to enhance the initial activity, and the other may be pulverized by either wet or dry milling but is required to be pulverized roughly in order to raise the content of the active ingredients in the formulation or enhance the residual activity, it was so hard to employ a process of kneading and granulating materials following to dry milling and a process of kneading and granulating materials following to wet milling for the production of a water dispersible granule formulation.